1. Toxicity of pigment blepharismin of Blepharisma japonicum-----we purified blepharismin and oxyblepharismin (the pigment generated from blepharismin under oxygen and light), and studied their toxicity and phototoxicity to several diiates. Blepharismin showed strong toxicity and phototoxicity to variety of ciliates, but B.japonicum was resistant to blepharismin. Oxyblepharismin also possessed toxicity and phototoxicity. The toxic properties of blepharismin and oxyblepharismin were compared with plant pigment, hypericin, and it was found that blepharismin and oxyblepharismin are characteristic in their strong intrinsic toxicity. In this study, the mechanism of chemical defense in B.japonicum was clarified ; B.japonicum possesses pigment blepharismin which is not toxic to Blepharisma itself but toxic to other ciliate and B.japonicum extrudes the pigments when cells are attacked.2. Structure and toxicity of possible defensive toxin in Climacostomum virens----- When carnivorous ciliate Dileptus margaritifer attacks C.virens , D.margaritifer retreated. The possible defensive toxin in C.virens was purified and the structure was determined. It was established as l, 3-dihydoxy-5-[(Z)-2'-nonenyl] benzene, and named Climacostol. The structure was confirmed by the total synthesis.3. Defensive function of trichocysts in Paramecium-----trichocysts in Paramecium are extrusomes for defense. In this study, we investigated the defensive function against variety of ciliates and other protozoans. Defensive function of trichocysts was remarkable against C.virens, Echinoshaerium akamae, E.nucleofilum, but it was not noticeable to Heliophrya erhardi (suctoria) and Amoeba proteus.